In radio communication systems, in particular in mobile radio networks, such as according to the UMTS standard (Universal Mobile Telecommunications System), the local position of a mobile radio communication device can be determined, in that one or more propagation times or propagation time differences of measuring signals between the base station in the location radio cell of the radio communication device which is to be located and/or between one or more base stations in adjacent radio cells to the location radio cell and the radio communication device which is to be respectively located are measured. The local position of the radio communication device which is to be located can be calculated from the measured measuring signal propagation times and the known position data of the base stations. This type of position determining is radio interface-based as the required signal measurements are carried out on the existing radio interface of the radio communication device which is to be respectively located.
A known locating measuring method is, in particular, what is known as RTT measurement (Round Trip Time). This will be schematically described in terms of principle with reference to FIG. 2. In FIG. 2 the positions of three base stations BS1, BS2, BS3 are each shown by a circle. These base stations receive radio measuring signals MS1, MS2, MS3 via the radio interface of a radio communication device which is to be located and which is situated at the position PO1. The respective base station BS1, BS2, BS3 can determine its respective distance from the radio communication device which is to be located from the propagation time of the respective measuring signal MS1, MS2, MS3. The propagation time of the respective measuring signal may be determined, for example, by forming the time difference between the starting time and receiving time of the measuring signal in the respective base station. The starting time of the respective measuring signal can in this case be sent with the measuring signal as a parameter, so it is made known to the base station. The determined difference between the starting time and the receiving time of the respective measuring signal corresponds to a range circle around the respective base station which shows the possible local position of the radio communication device which is to be located. In the case of the three propagation time measurements in FIG. 2, three range circles RTT1, RTT2, RTT3 result with a common point of intersection which indicates the local position PO1 of the radio communication device which is to be located.
A further measuring method is what is known as the OTDOA method (Observed Time Difference of Arrival). In this case the propagation time difference of two measuring signals, which are emitted by at least two adjacent base stations, is determined in the radio communication device which is to be located. As the local positions of the base stations is known, a hyperboloid may be established from the measured propagation time difference as a local curve of constant distance from the two known local positions of the two base stations. At least two propagation time difference measurements are preferably carried out in this case. This is shown in FIG. 3 where the difference between the propagation times of measuring signals MS1*, MS2*, which are sent by the two base stations BS1, BS2, are measured with the aid of the radio communication device which is to be located. This first propagation time measurement, together with the known local position of the two base stations BS1, BS2, produces a first hyperboloid HYP12 as a possible location of the radio communication device. The difference between the propagation time of the measuring signals MS1*, MS3* of the two base stations BS1, BS3 is measured in a corresponding manner and together with the known local positions of these two base stations BS1, BS3 a second hyperboloid HYP13 is determined. With the aid of the measuring signal MS3* a further range circle RTT3 is determined using the RTT method. Thus a clear point of intersection results for the three location measuring curves HYP12, HYP13, RTT3 and thus the location PO1 of the radio communication device which is to be located.
In the case of these known radio interface-based position determinations, the accuracy of the calculated position depends on a large number of factors. However, in principle, the following tends to apply: the more range circles (a range circle is defined by a known local position and a signal propagation time, see FIG. 2) and/or hyperboloids (a hyperboloid is defined by two local positions and the difference between two signal propagation times, see FIG. 3) there are available for calculating the position of the radio communication device which is to be respectively located, the more accurate the position thereof can be ascertained.